Retinal cone photoreceptors mediate daylight vision and color sensations. These cells absorb light and transduce it into an electrical response that is ultimately transmitted to visual neurons in the brain. We are interested in cone transduction and have examined it in cones from cynomolgus monkeys. These cells give unusual light responses that have not been observed in cones of other animals (except man). We are interested in the molecular mechanism that produces these responses, in particular how dynamic changes in intracellular calcium are involved. To study this we enucleate eyes from macaques being euthanized, dissect the retinas, and then dissociate and record electrically from isolated photoreceptors. We have obtained useful measures of sodium-calcium exchanger currents in these cells, and analysis of these currents has allowed us to find the time course of changes in intracellular calcium. These results have never before been obtained and advance our understanding of transduction in these cells.